Answer
$$-3\, or, \ 2.5 .$$
Work Step by Step
For the equation $2x^2 +x-15 = 0$, we use the quadratic formula as follows $$ x=\frac{-b \pm \sqrt{b^{2}-4 a c}}{2 a}, \\ a=2, \quad b=1, \quad c=-15 .$$ That is, $$ x=\frac{-1 \pm \sqrt{1+120}}{4 }=-3\ , or, \ 2.5 .$$
